Impact of preceding crop on alfalfa competitiveness with weeds

Abstract

AbstractOrganic producers would like to include no-till practices in their farming systems, but they are concerned about managing weeds without tillage. We are seeking to develop a continuous no-till system for organic farming, based on a complex rotation that includes a 3-yr sequence of alfalfa. In this study, we evaluated impact of preceding crop on weed infestation in alfalfa. Alfalfa was established with no-till following spring wheat, corn or soybean. The study involved a 4-yr interval, with weed dynamics measured in the fourth year. Alfalfa established after soybean suppressed weeds more than alfalfa established after spring wheat or corn. Weed biomass in alfalfa following spring wheat was 18% of the plant community, but only 1% when alfalfa followed soybean and 6% when alfalfa followed corn. Weed biomass increased because alfalfa density following spring wheat was only 71% of alfalfa following soybean. Weeds such as downy brome (Bromus tectorumL.) and dandelion (Taraxacum officinaleWeber) were able to establish and produce biomass where alfalfa stand was sparse. Alfalfa forage yield across 3 yr was also higher following soybean than either spring wheat or corn. Alfalfa competitiveness with weeds can be improved by choice of preceding crop.